The present invention relates to a control device for a stepping motor.
One conventional stepping motor connects with a drive system including a member which rebounds resiliently for a small distance in a direction opposite to that of its driven direction owing to its resiliency when an external driving force is interrupted. This kind of stepping motor is used in an electronic typewriter, for example, so as to rotate the platen.
Referring to FIG. 5, a gear 6 engages with another gear 5 of the conventional stepping motor so that a rotational axis 4 of the stepping motor is connected with a transmission shaft (not shown) of the platen. A tooth 6a of the gear 6 is bent due to the load of the platen when the stepping motor is stopped. If the resiliency of the resilient tooth 6a is greater than a restraining force of the stepping motor, the gear 5 is rotated backward, as shown by an arrow A in the drawing. Under such condition, the stepping motor stops with the rotor displaced from an appropriate position. For this reason, the control device for the stepping motor with a weak restraining force, in particular, cannot sequentially rotate the rotor properly, thus sometimes resulting in step-out. The same problem occurs with regard to a stepping motor which moves the carriage of the typewriter back and forth by means of a resilient member such as a wire.